Isobar

http://hsc.csu.edu.au/primary_ind/prim_ind_240/compulsory/RTE2503A/3264/reading_weather_maps.htm

Isobars are a weather mapping technique to display air pressure, this can be used to help predict weather patterns. This is a map of Australia displaying the different air pressures surrounding high and low pressures as well as a tropical cyclone.